I need an anti virus

Any suggestions, cause I'm really getting sick and tired of formating this pos. I'm a pc idiot so something simple would be best and also free. I was running Mcafee (free) but on the day I switched ISP's, it gave me a virus. So I formatted once again. BTW I'm running XP.

im supose to get an program that cost 80$ from a friend dont know name of the program but its for windows 7 i think. I can look around see want I can find idk if you want cracked virus protection programs? if you do let me know ill do some searching